Sugars halogen addition

The increased availability of methods for the preparation of unsaturated sugars107 has stimulated interest in addition reactions of these compounds the use of unsaturated carbohydrate derivatives as precursors for specifically halogenated sugars has been widely exploited. 

Many other examples of the use of halogenated sugar analogues in glycoprotein research could be cited, including additional rational approaches to chemotherapeutic agents. These are discussed in more detail in recent reviews147,151. 

The addition of halogen fluoride to unsaturated carbohydrates gives a mixture of cis- and /ra .t-adducts similar to other electrophilic additions to unsaturated sugars. 

The action of the halogens on the simple sugars may be obscured for several reasons. The nature of some of the oxidants may be difficult to determine the transient character of several of the oxyhalogen acids often serves to hide the real mechanism of the oxidation. In addition, it is often rather difficult to isolate the oxidation products of a sugar, especially when more than one product is produced in a reaction or when suitable analytical methods have not been developed. 

Miss Frush and IsbelF used crystalline heptaacetyl-a-neolactosyl chloride in the Konigs-Knorr reaction under conditions identical with those described for pentaacetyl-a-D-(a)-guloheptosyl bromide, with the exception that the reaction time was increased to seventy-two hours. Acid and alkaline hydrolysis of the reaction solution showed that only about 70% of the original sugar was present, and that this was almost completely in the form of the orthoester. By extraction of the silver residues with chloroform, a halogen-free sirup was obtained, from which short rectangular crystals separated upon addition of methyl alcohol. This substance was methyl /3-neolactoside heptaacetate, which exhibited the expected normal behavior. 

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